1. Field of the Invention
The present invention relates to an abnormality diagnosis device of an internal combustion engine for diagnosing a clogging abnormality of a PCV passage (positive crankcase ventilation passage) recirculating a blow-by gas to an intake system.
2. Description of Related Art
Conventionally, there have been proposed various devices for diagnosing an abnormality related to a PCV passage (for example, refer to Patent document 1: JP-A-2007-2838). According to Patent document 1, an air quantity upstream of a connection between an intake system and the PCV passage in an intake passage is sensed with an air flow meter. The abnormality in the PCV passage is diagnosed based on a result of comparison between the sensed air quantity and a determination value. If the PCV passage breaks or disengages from the intake system, an outside air flows into the intake system via the broken portion or disengaged portion, so the air quantity (average flow rate) flowing upstream of the connection between the intake system and the PCV passage decreases. In consideration of this point, according to Patent document 1, the intake air quantity sensed with the air flow meter is monitored to detect an air leakage resulting from the breakage of the PCV passage, the disengagement of the PCV passage from the intake system or the like.
The technology of Patent document 1 diagnoses the air leakage due to the breakage of the PCV passage and the like but cannot diagnose a clogging abnormality of the PCV passage. In the case of the air leakage due to the breakage of the PCV passage and the like, the outside air flows in via the portion of the air leakage, so the air quantity (average flow rate) introduced into the intake system via the PCV passage increases. If the clogging abnormality is caused in the PCV passage by incorporation of extraneous matters and the like, a diameter of the PCV passage decreases and therefore the air quantity (average flow rate) introduced into the intake system through the PCV passage does not increase. Therefore, in the case of the clogging abnormality, the increase or decrease of the average flow rate as in Patent document 1 does not appear upstream of the connection between the intake system and the PCV passage. Therefore, the clogging abnormality cannot be diagnosed with the above-described method.